Xenogeneic renal transplants from MGH Gal-knockout (GaIT-KO) miniature swine to baboons performed prior to 2005 using chronic immunosuppressive regimens, survived longer (on average 29 days) than similar xenogeneic renal transplants from other sources of GaIT-KO swine, performed at several other research centers (ca. 15 days) (Yamada et al., Nat Med 2005; 11:32-34; Zhong et al., Transplantation 2003; 75:10-19). Transplants at MGH using MGH GaIT-KO donors and a tolerance-inducing regimen (i.e., thymokidney transplants) survived an average of 51 days (Yamada et al., 2005, supra; Griesemer et al., Am J Transplant 2009; 9:2669-2678). Though length of survival of the grafted materials is crucial, the reason for this much superior performance was not known.